Distributing information over a network

ABSTRACT

Distributing information over a network is disclosed. Nodes are grouped into regions. Preferred nodes are designated. A source of content to be delivered to a preferred node using a preferred algorithm is indicated to at least one preferred node. At least one common node is assigned the preferred node as a relay of information.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/859,428 entitled CONTENT DISTRIBUTION filed Nov. 15, 2006 whichis incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Users are increasingly using networks such as the Internet to accesscontent, such as video files and live streaming/video on demand content,via client machines. Such content is often large, time sensitive, orboth. As demand for such content increases, there are challenges indistributing that content efficiently and with high quality.

Two ways that content owners can distribute content are by using theirown servers or buying the service of a content delivery network (CDN).In the later case, content owners typically contract with CDNs toprovide content to clients, e.g., in exchange for a fee. Requests byclients for content are directed to CDN nodes that are close by, e.g.,the fewest hops away from the clients. The client then downloads thecontent from the appropriate CDN node. In both cases, content isdistributed by servers, owned by either the content owner directly orthe CDN. Unfortunately, as demand on server capacity increases (e.g., asthe content size gets bigger and/or the number of requests to thecontent increase), meeting that demand by increasing capacity is oftenvery expensive, requiring a larger number of servers or more powerfulservers to be deployed.

Another way that content can be distributed is through use ofpeer-to-peer (P2P) systems. In a typical P2P scenario, a node downloadscontent from the system, and also uploads content to other nodes. In ahybrid content distribution system, a fraction of the content istransmitted by the servers and the rest is transmitted by nodes usingtheir uplink capacity. Unfortunately, ISPs are facing increased networkcongestion from P2P and hybrid content distributions. One reason is thattraditional P2P approaches rely on peers making independent routingdecisions based on local information. This is approach is typicallytaken so that there is no single scalability bottleneck and no singlepoint of failure. Unfortunately, such an approach may result in poorperformance, inefficient resource utilization, and other shortcomings.

Therefore, it would be desirable to have a better way to distributeinformation over a network.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is an illustration of an embodiment of a system for distributinginformation over a network.

FIG. 2 is an illustration of nodes grouped into regions according to oneembodiment.

FIG. 3 is an illustration of nodes designated as preferred nodesaccording to one embodiment.

FIG. 4 is an illustration of nodes designated as second level nodes in athree-level hierarchy according to one embodiment.

FIG. 5 is an illustration of nodes designated as common nodes in athree-level hierarchy according to one embodiment.

FIG. 6 is a flow chart illustrating an embodiment of a process fordistributing information over a network.

FIG. 7 is an illustration a representation of the management of nodes ina three-level hierarchy according to an embodiment.

FIG. 8 is an illustration of an embodiment of a system havingresilience.

FIG. 9 is a representation of an example of a heartbeat.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess, an apparatus, a system, a composition of matter, a computerreadable medium such as a computer readable storage medium or a computernetwork wherein program instructions are sent over optical orcommunication links. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. A component such as a processor or a memory described asbeing configured to perform a task includes both a general componentthat is temporarily configured to perform the task at a given time or aspecific component that is manufactured to perform the task. In general,the order of the steps of disclosed processes may be altered within thescope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

FIG. 1 is an illustration of an embodiment of a system for distributinginformation over a network. In the example shown, clients 170-184 areused to access content, such as audiovisual content (e.g., movies,songs, television shows, sporting events, games, etc.) that is owned bycontent owners. Clients can include personal computers (e.g., 170),laptops (182), and cellular phones/personal digital assistants (178), aswell as other types of information appliances (not shown) such asset-top boxes, game consoles, broadband routers, file servers, videoservers, and digital video recorders, as applicable. As used herein,nodes can include clients and servers, all of which can be peers—such asneighbors, parents, and children.

The clients shown are used by subscribers to various Internet serviceproviders (ISPs). For example, clients 170, 172, and 174 are subscribedto SP1 (122), while clients 176, 178, and 180 are subscribed to SP2(124) and clients 182 and 184 are subscribed to SP3 (126).

One typical goal of content owners is for their content to reach theircustomers (who likely subscribe to different networks) in an efficient,economic manner. In the example shown, a movie studio has contractedwith content distributor 142 to provide downloadable copies of itsfilms. Similarly, a soccer league has contracted with contentdistributor 144 to provide season pass holders with access to livestreams of matches.

Content distributor 142 has a data center that is provided with networkaccess by backbone ISP 132. Though represented here by a single node(also referred to herein as a “CDN node”), content distributor 142 maytypically have multiple data centers (not shown) and may make use ofmultiple backbone or other ISPs. Content distributor 144 has a datacenter that is provided with network access by backbone ISP 134.

Control center 102 gathers status information from nodes and dynamicallyconstructs and adjusts distribution topologies among nodes. As describedin more detail below, in some embodiments nodes provide lightweightheartbeats to control center 102 with information about their resourceavailability, their performance experience when downloading from orstreaming to other clients, etc. The distribution topology constructedby control center 102 takes into consideration the network trafficimplications of the peers it associates and can provide quality ofservice, cause resources to be used efficiently, converge quickly in thepresence of network changes, and satisfy network-wide constraints. Thecontrol center sends commands back to the nodes instructing them whereto obtain content, and including in some embodiments instructionsindicating which protocols to use.

Suppose a user of client 170 desires to watch a soccer match live (asthe game occurs) and to simultaneously download a movie for watchingafter the match ends. Control center 102 might optimize delivery of thelive event over the delivery of the movie—selecting peers (and/or“neighbors” and/or “parents/children”) accordingly.

In various embodiments, nodes run software that monitors resourceavailability and network congestion and implements data replication andforwarding. The coordinator may consider a variety and/or combination offactors such as network conditions and resource availability, whichfiles are being distributed, the number of clients, the nature of thecontent (e.g., live event vs. file; free content vs. premium or adsupported content), and the nature of the client (e.g., whether the userhas paid for premium service). The coordinator can also coordinatemultiple file transfers to different nodes (e.g., where a user of client176 wants to download the movie, a user of client 178 wants the sportingfeed, and a user of client 180 wants both).

In the example shown, control center 102 includes a plurality ofdelivery coordinator managers (DCMs) 104, a content directory 106, aclient manager 108, and a service manager 110. Client manager 108receives heartbeats from nodes that include state information and inturn distributes information to other components. When a client requestscontent (such as might be triggered by a user clicking on a “watchtoday's soccer match live” link in a browser), the client contactscontrol center 102 to determine if a DCM is managing that content (alsoreferred to herein as a “channel”) in a region, consulting contentdirectory 106. A region includes a set of nodes that are grouped by avariety of criteria including but not limited to network topology,geographic proximity, administrative domain (e.g., autonomous system,enterprise), and network technology (e.g., DSL, cable modems, fiberoptic). If no DCM is currently responsible for the content, servicemanager 110 configures a DCM as appropriate. Once a DCM for the contentand region that the client is in exists, the client is provided withinstructions for downloading the content, e.g., from a specific pair ofneighbors.

In the example shown, a single control center 102 is used. Portions ofcontrol center 102 may be provided by and/or replicated across variousother modules or infrastructure depending, for example, on factors suchas scalability and availability (reducing the likelihood of having asingle point of failure), and the techniques described herein may beadapted accordingly. In some embodiments control center 102 isimplemented across a set of machines distributed among several datacenters. As described in more detail below, in some embodiments controlcenter 102 uses a Resilience Service Layer (RSL) which ensures that thecontrol center service is not disrupted when/if a subset of controlmachines fail or a subset of data centers hosting the control center aredisconnected from the Internet.

FIG. 2 is an illustration of nodes grouped into regions according to oneembodiment. Nodes are grouped into regions based on the natural networkboundaries and policy domains. Examples of such regions includeautonomous systems (AS)es, and large organizations such as universities.One goal of grouping nodes into regions is to optimize traffic within aregion—such as by being in close proximity (and likely sharing a fastlink), and/or by having similar characteristics (e.g. a group of DSLsubscribers vs. a group of cable modem subscribers). The partitioningchanges slowly over time, and can be efficiently replicated as needed.In the example shown, clients 210-222 and 280 are grouped into region202, clients 230-234 and 282 are grouped into region 204, and clients262-266 and 284 are grouped into region 206.

In some embodiments control center 102 implements a multi-scaledecomposition (MSD) algorithm which partitions the computation of alarge distribution topology into multiple computation tasks that managea smaller number of peers (e.g., thousands to tens of thousands).

In the following examples described herein, MSD is used to organize allthe nodes that subscribe to a channel (data stream) into a three-levelhierarchy. The top two levels use distribution protocols that areoptimized primarily for resilience, while the bottom level usesdistribution protocols that optimize for efficiency. Robustness andefficient bandwidth utilization can be optimized for as applicable. Inother embodiments, nodes are grouped into hierarchies of other depths.For example, in a two-level hierarchy nodes that might be collectivelypresent in the top two tiers of a three-level hierarchy may be collapsedinto a single top level, nodes that would be present in the second tierof a three-level hierarchy may be split between the two levels of thetwo-level hierarchy, or nodes that would be present in the second tierof a three-level hierarchy may all be relegated to the bottom level.Four-level and other hierarchies can be used and the techniquesdescribed herein adapted as applicable.

As described in more detail below, nodes occupying one level of thehierarchy may communicate using distribution algorithms different fromnodes occupying another level of the hierarchy. Different groups ofnodes may also communicate between levels (and at the lower levelsamongst themselves) using protocols optimized for factors such asnetwork conditions, resource usage, etc. For example, one top level nodemay communicate with a group of bottom level nodes using a protocoloptimized for delivering information to clients that make use of dialupconnections (where the bottom level nodes connect to the Internet usingmodems), while a group of bottom level nodes may communicate amongstthemselves using a protocol optimized for communication among cablemodem subscribers of a particular telecommunication company (where thebottom level nodes are all subscribers of that particular cable modemservice).

FIG. 3 is an illustration of nodes designated as preferred nodesaccording to one embodiment. In the example shown, nodes 214, 234, and264 are designated by control center 102 as preferred nodes. They areincluded in the top level of a three-level hierarchy of nodes (302),which includes a few high capacity and stable nodes from each region(e.g., regions 280-284 as shown in FIG. 2) which has peers subscribingto the channel. In this example, high capacity nodes include nodes whoseoutput capacity is larger than the rate of the data being distributed.In some embodiments, if a region has no high capacity nodes, nodes maybe provided (e.g., by the entity that owns control center 102) on behalfof that region located in a data center close to that region. Such anode is referred to herein as a waypoint server. In the example shown inFIG. 1, waypoint server 146 has been provided by the owner of controlcenter 102. The waypoint server can also be provided by a third-party.Nodes may also be provided by instructing high quality clients to obtaincontent that they would not otherwise request. For example, suppose theuser of client 214 desires to watch a movie from content distributor 142but is not interested in the soccer content provided by contentdistributor 144. If needed, in addition to serving as a preferred nodefor the movie content, client 214 can also be configured to serve as apreferred node for the sports content, as applicable. As described inmore detail below, the nodes in tier 302 communicate with one anotherusing a highly resilient protocol to deliver data with littledegradation, even in the face of multiple simultaneous failures.

FIG. 4 is an illustration of nodes designated as second level nodes in athree-level hierarchy according to one embodiment. The second levelincludes clusters connected to the top level. A cluster includes thehigh capacity nodes belonging to a single region. In the example shown,clients 212, 216, 220, 232, and 262 are included in the middle level ofthe three-level hierarchy of nodes (402). While the goal of the secondlevel as with the first level is robustness, the degree of redundancyused at the second level (e.g., to ensure data delivery) is typicallylower than at the top level. As described in more detail below in someembodiments the nodes in tier 402 communicate using a variant of thedistribution protocol implemented in tier 302.

FIG. 5 is an illustration of nodes designated as common nodes in athree-level hierarchy according to one embodiment. In the example shown,nodes 210, 218, 222, 280, 230, 282, 284, and 266 are designated bycontrol center 102 as common nodes. They are included in the bottomlevel of a three-level hierarchy of nodes (502), which includes mainlyof low-capacity nodes (in this example, nodes whose output capacitiesare lower than the data rate). Each cluster of nodes in level 502 sharesat least a few high capacity nodes with the second level, ensuring thateach cluster has several high-quality data stream feeds. As described inmore detail below, the distribution algorithm used among nodes in level502 is optimized for efficient resource utilization.

FIG. 6 is a flow chart illustrating an embodiment of a process fordistributing information over a network. The process begins at 602 whennodes are grouped into regions. In some embodiments the processing ofportion 602 of FIG. 6 is performed by control center 102. In the exampleshown in FIG. 2, nodes 210-284 are grouped into regions at 602.

At 604 preferred nodes are designated. In some embodiments theprocessing of portion 604 of FIG. 6 is performed by control center 102.In the example shown in FIG. 3, nodes 214, 234, and 264 are designatedas preferred nodes at 604.

At 606 a source of information to be delivered to a preferred node usinga preferred algorithm is indicated. For example, at 606 node 214 (whichis in possession of a full copy of a particular piece of content) isindicated as a source of that content to node 234. At 606, nodes havingonly portions of content may also be designated as sources of thoseportions of content. One example of a preferred algorithm is a floodingalgorithm with duplicate elimination. The algorithm first creates anoverlay mesh topology where the capacity of each virtual link is greaterthan the stream rate and the mesh forms a c-connected graph. When a nodeA receives a new packet, i.e., a packet that it has not seen so far,from neighbor N, node A sends a copy of the received packet to each ofits neighbors, except N. This algorithm ensures that all nodes will getevery packet sent by the source even when as many as c-1 nodes failsimultaneously. Another example of a preferred algorithm is a simpletree distribution algorithm, which might be used if all nodes at thislevel are highly stable.

At 608 the preferred node is assigned as a relay of information to acommon node. For example, at 608 client 230 may be instructed toretrieve portions of content from node 220.

FIG. 7 is an illustration a representation of the management of nodes ina three-level hierarchy according to an embodiment. In the exampleshown, all nodes in the top level (302) are managed by a single DCM suchas DCM 710 (and as represented in FIG. 7 by dashed lines). One role ofthe DCM is to maintain an accurate distribution topology of the nodes atthis level. The DCM computes the distribution topology based on theclient available resources, the connectivity to the Internet (e.g., whatkind of NAT/firewall the client is behind), congestion in the network,and various network-wide policies. In various embodiments, DCM 710 islogically a single DCM but is implemented across a plurality of physicalDCMs.

In the example shown, each cluster of nodes in the third level (502) ismanaged by a DCM, such as DCM 706 (and as represented in FIG. 7 bydotted lines). The clusters change dynamically as nodes join and leavethe distribution graph. Small clusters are dynamically merged, and largeclusters are split. Since this level includes the vast majority of nodesin the data group, the distribution algorithm can be optimized forefficient resource utilization.

One example of an efficient distribution topology at the third level isa multi-tree. In the multi-tree case, the stream is divided into severalsubstreams k, where substream i includes packets with sequence numbersk*j+1; j≧0. Each substream will have a rate of R/k, where R is theoriginal stream rate. For each substream, the algorithm builds asub-tree. Each node is an interior node in one sub-tree, and a leaf nodein every other sub-trees. A multi-tree algorithm can use the uploadcapacity of a node as long as this capacity is larger than thesub-stream rate. The tree building algorithm can be optimized forvarious objective functions such as minimizing each sub-tree depth orminimizing the distance between the child and its parents (every nodewill have one parent in each sub-tree), and subject to the capacityconstraints of the clients, and performance and policy constraints.

In some embodiments a multi-tree topology is built by building trees oneat a time. To build such a tree, one could use a greedy algorithm thatadds nodes to a sub-tree one by one, making sure that none of theadditions violates the existing constraints. Several heuristics can beused to increase the probability that the greedy algorithm succeeds. Anexample of such heuristic is to select the node with the highestcapacity, or fewest constraints, to add next.

In the example shown, each cluster of nodes in the second level (402) ismanaged by a DCM, such as DCM 702 (and as represented in FIG. 7 by thedotted dashed line). One goal of the distribution algorithm at thesecond level is to maintain quality of service, even if this incurs ahigher overhead. An example of a distribution algorithm used by level402 is to modify the multi-tree algorithm used at level 502 as follows.Instead of splitting the stream into k substreams, the algorithm useserasure codes to create k+n substreams, such that any k substreams outof the n+k substreams would be enough to reconstruct the originalstream. The algorithm takes each group of k consecutive packets (i.e.,packets with sequence numbers k*j, k*j+1, . . . , k*j+n−1; j≧0), anduses erasure codes to create k+n packets such that receiving any kpackets will be enough to reconstruct the original k packets. Thealgorithm constructs a sub-tree for each sub-stream similar to themulti-tree algorithm at the third level.

In some embodiments the algorithms running in different clusters oflevel 402 use different redundancy factors to account for the quality ofthe underlying network. For example, if all hosts in a cluster at thesecond level are in Japan a low redundancy factor can be used, while ifall hosts are in India a higher redundancy factor might be used (as thenetwork is in general less reliable). Similarly, a higher redundancyfactor could be used for a deployment in a cable modem environmentrelative to a DSL environment.

FIG. 8 is an illustration of an embodiment of a system havingresilience. When client 182 starts (e.g., after booting), daemon 802 isinitiated, which communicates information between client 182 and controlcenter 102. In the example shown, control center 102 includes servers810-814 each of which runs services such as by providing DCMfunctionality. Each DCM is mapped by a logical identifier. ResilienceService Layer (RSL) 804 maintains mappings between servers 810-814 andtheir logical identifiers. If RSL 804 detects that a server, such asserver 810 has failed, the RSL maps another DCM (such as a backup DCM orspare DCM not pictured) to that logical identifier. Similarly, ifprimary service manager 806 fails, it is replaced by backup servicemanager 808.

From the perspective of a client, such as client 188, a failover fromDCM 810 to its replacement is transparent. Clients, such as client 188,periodically provide their state to DCMs (e.g., through heartbeats sentvia network 816), and thus if a DCM fails (and is replaced), thereplacement DCM is provided by the client with state information thatindicates to the replacement DCM such details as the neighbors from/towhich the client is exchanging content.

FIG. 9 is a representation of an example of a heartbeat. The heartbeatmessages contain all necessary information required by the DCM toconstruct a global view of the distribution topology. In someembodiments each heartbeat message sent by node A contains the sequencenumbers of the last packets received by A from each of its parents, aswell as the sequence numbers of the last packets sent by A to each ofits children. This information allows the DCM not only to construct thedistribution topology, but also to determine which links are congestedby comparing the sequence numbers of the packets sent/received by everynode at the end of every heartbeat interval. In the example shown,heartbeat 900 includes the following information. The ClientID is aunique identifier of the client sending the heartbeat. The Heartbeat Seqis the sequence number of the heartbeat. P1, . . . , Pk represent thelist of parents of ClientID. Parent Pi sends stream i to ClientID, where1≦i≦k. C1, . . . , Cm represent the list of children of ClientID. TheLocal Timestamp is the timestamp at the client at the time the heartbeatwas generated. Buffersize Si is the current buffer size for stream i,where 1≦i≦k. Timestamp TPi is the timestamp of the last packet receivedfrom parent Pi. Timestamp CTj is the timestamp of the last packet sentto child Cj, where 1≦j≦m.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A system for distributing information over anetwork, including: a processor; and a memory coupled with theprocessor, wherein the memory is configured to provide the processorwith instructions which when executed cause the processor to: groupnodes into regions; designate a first subset of nodes as preferred nodesand a second subset of nodes as common nodes; indicate to a preferrednode in the first subset a source of content, wherein a preferreddistribution algorithm is selected to be used in communicating thecontent between the source and the preferred node based at least in parton the preferred node's designation; and assign the preferred node as arelay of information to a common node in the second subset, wherein theinformation relayed between the preferred node and the common node iscommunicated using a distribution algorithm that is selected based atleast in part on the common node's designation and that is differentfrom the preferred algorithm selected to be used in communicating thecontent between the source and the preferred node.
 2. The system ofclaim 1 wherein the preferred algorithm optimizes for robustness overefficiency.
 3. The system of claim 1 wherein the algorithm used to relayinformation from the preferred node to the common node is based at leastin part on the region into which the common node is grouped.
 4. Thesystem of claim 1 wherein information is relayed to the common nodeusing an algorithm optimized for efficiency over robustness.
 5. Thesystem of claim 1 wherein the preferred nodes are of a first type, andwherein the memory is further configured to provide the processor withinstructions which when executed cause the processor to designatepreferred nodes of a second type.
 6. The system of claim 1 furtherincluding a delivery coordinator manager configured to select a deliveryalgorithm to be used between two nodes.
 7. The system of claim 1 furtherincluding a relay configured to associate one of the regions into whichnodes are grouped with a delivery coordinator manager.
 8. The system ofclaim 1 further including a delivery coordinator manager associated witheach region into which nodes are grouped.
 9. The system of claim 1wherein nodes are designated as preferred nodes based at least in parton their historical performance.
 10. The system of claim 1 wherein thememory is further configured to provide the processor with instructionswhich when executed cause the processor to detect a failure of a firstdelivery coordinator manager and reassociate nodes associated with thefailed delivery coordinator manager with a second delivery coordinatormanager.
 11. The system of claim 10 wherein the second deliverycoordinator manager is configured to reconstruct state information fromheartbeats provided by nodes.
 12. The system of claim 10 wherein thenodes are reassociated with the second delivery coordinator managerunobtrusively.
 13. The system of claim 1 wherein the nodes areconfigured to transmit a heartbeat that includes state information. 14.The system of claim 1 wherein the nodes that have been grouped into aregion are in possession of a logical identifier of a deliverycoordinator manager.
 15. The system of claim 1 wherein nodes are groupedinto prespecified regions based on policies and the last knowncharacteristics of the nodes.
 16. The system of claim 1 wherein at leastone preferred node is owned by a third party.
 17. The system of claim 1wherein the memory is further configured to provide the processor withinstructions which when executed cause the processor to evaluate nodesfor selection as preferred nodes on a recurring basis.
 18. The system ofclaim 1 wherein the information relayed from the preferred node to thecommon node is a portion of a first content and wherein the memory isfurther configured to provide the processor with instructions which whenexecuted cause the common node to receive a portion of a second contentsimultaneously with the receipt by the common node of the portion of thesecond content.
 19. The system of claim 1 wherein the informationdelivered from the preferred node to the common node is a portion ofcontent which a user of the common node wishes to consume, and which nouser of the preferred node wishes to consume.
 20. The system of claim 1wherein at least one preferred node is a client.
 21. The system of claim1 wherein at least one preferred node is a server.
 22. The system ofclaim 1 wherein the preferred node and the common node are each presentin a node hierarchy and wherein the preferred node and the common nodeare at respective different levels of the hierarchy.
 23. The system ofclaim 1, wherein the preferred distribution algorithm includes aprotocol optimized for a set of factors including at least one of anetwork condition and resource usage.
 24. The system of claim 1, whereinthe first subset and the second subset of nodes are designated aspreferred nodes and common nodes, respectively, based at least in parton an evaluation of a capacity of the nodes.
 25. The system of claim 1,wherein the preferred nodes and the common nodes are configured tocommunicate using different distribution algorithms.
 26. The system ofclaim 1, wherein the information relayed to the common node via thepreferred node includes a portion of the content delivered to thepreferred node by the source.
 27. A method for distributing informationover a network, comprising: grouping nodes into regions; designating afirst subset of nodes as preferred nodes and a second subset of nodes ascommon nodes; indicating to a preferred node in the first subset asource of content, wherein a preferred distribution algorithm isselected to be used in communicating the content between the source andthe preferred node based at least in part on the preferred node'sdesignation; and assigning the preferred node as a relay of informationto a common node in the second subset, wherein the information relayedbetween the preferred node and the common node is communicated using adistribution algorithm that is selected based at least in part on thecommon node's designation and that is different from the preferredalgorithm selected to be used in communicating the content between thesource and the preferred node.
 28. A computer program product fordistributing information over a network, the computer program productbeing embodied in a non-transitory computer readable medium andcomprising computer instructions for: grouping nodes into regions;designating a first subset of nodes as preferred nodes and a secondsubset of nodes as common nodes; indicating a preferred node in thefirst subset a source of content, wherein a preferred distributionalgorithm is selected to be used in communicating the content betweenthe source and the preferred node based at least in part on thepreferred node's designation; and assigning the preferred node as arelay of information to a common node in the second subset, wherein theinformation relayed between the preferred node and the common node iscommunicated using a distribution algorithm that is selected based atleast in part on the common node's designation and that is differentfrom the preferred algorithm selected to be used in communicating thecontent between the source and the preferred node.